The descending systems comprised of medullary reticulospinal and lateral vestibulospinal neurons have been shown responsible for facilitating deep back muscle contraction in the well analyzed reproductive behavior, lordosis. Properties of these descending systems and the deep back muscles are remarkably congruent with lordosis behavior requirements, and have proven unusually accessible to physiological and cellular analysis. What is occurring chemically in these neurons upon stimulation, under conditions where electrical activation leads to deep back muscle contraction? We will answer part of this question using immunocytochemistry and in situ hybridization for expression of early response genes since these are exquisitely responsive to neuronal stimulation. We will study c-fos in medullary reticulospinal and lateral vestibulospinal cells, as well as deep back muscle motoneurons, to correlate expression with back muscle contraction as a function of brainstem stimulation parameters. Most important, fos expression will be followed during use-dependent facilitation, as well as during interactions with somatosensory input or midbrain central gray stimulation. Parallel studies will be carried out with c-jun and NGFI-A. Can we discover any consequences of c-fos expression in neurons? We can achieve overexpression in specific neuronal groups using our defective viral vector and can achieve underexpression using antisense sequences. Each of these techniques has been worked out in our lab. We will study the consequences of each of these for stimulated deep back muscle EMG as well as for subsequent enkephalin and substance P expression in medullary reticular cells. These experiments will give new information on how early response genes could participate in neuronal stimulation leading to an easily studied reproductive behavior.